Films are used in the packaging industry, whereby both mono films and composite films are used.
The used films are thereby printed in order to provide information on the product, the producer or the trademark to the consumer and in order to create an aesthetic effect. Besides conventional printing methods, for example gravure printing, digital printing becomes more important and is used on labels, paper applications or so called shrink-sleeves.
However, films, in particular composite films, which are sealable and are sealed during the packaging process, have special requirements concerning the mechanical and thermal stability of the print image, which cannot be fulfilled with conventional digital printing methods and devices.
Normally, these films have typically been printed so far with gravure printing or flexography methods, which is however elaborate.
Using digital printing methods has only been possible so far, if the printing takes place on the inner side of the print substrate of composite films. However, further production processes, for example laminating, curing etc., are then required.
Thus, it would be desirable to provide a method, which enables printing on the outside of films, in particular composite films, and thereby using digital printing methods.
Digital printing of films is generally known. For example, Hewlett Packard offers a digital printing device called Indigo, which is in general suitable for printing of films, too. This device performs a corona pretreatment of the printing side, applies then a primer based on an aqueous solvent and finally digitally prints on the film.
However, films printed in this manner do not provide the required thermal and mechanical stability, which is expected for sealable films.
The problem to be solved by the present invention is providing a method for digital printing with improved thermal and mechanical stability, which can be used for sealable films as well.